RoboteQ AX2550/2850 Using the Encoder to Measure Speed

AX2500/2850 Motor Controller User’s Manual 139

Using the Encoder to Measure Speed

Using the Encoder to Measure Speed

The encoder module will automatically compute rotation speed for each encoder. The

resulting measured speed is a value ranging from 0 to + 127 and 0 to -127, where 127 rep-

resent a relative ratio of a maximum speed value chosen by the user.

For example, if the encoder module is configured so that the highest measured speed

value is 3,000 RPM, then a reading of 63 (127/2) would be 1,500 RPM.

The relationship between the measured speed and the actual speed is a factor of two vari-

able parameters: a Time Based period value stored inside the Encoder module and the

Encoder’s number of Pulses per Revolution. Note: the Encoder’s number of Pulses per

Revolution is not stored in the controller.

The Time Base is a number of 256us time intervals between two counter reads.

A simple procedure is included in the Roborun PC utility to easily determining and set

these parameters.

For information, the exact formula is shown below:

Measured Speed Value = RPM * PPR * 4 * (Time Base+1) * 256 / (60 * 1000000)

or Measured Speed Value = RPM * PPR * (Time Base + 1) / 58593.75

Example: a motor spinning at 1,000 RPM, with an encoder with 200 Pulses per Revolution,

and a Time Base set at 4 will produce the following measurement:

1000 *200 * (4 + 1) / 58593.75 = 17

The same formula modified to show the actual RPM at a given Measure Speed Value is as

follows:

RPM = Measured Speed Value * 60 * 1000000 / (PPR * 4 * 256 * (Time Base+1))

or RPM = Measured Speed Value * 58593.75 /((Time Base + 1) * PPR)

In our example, a measured speed value of 127 correspond to the following measurable

max actual RPM values

RPM at Max Measurable Speed Value = 127 * 58593.75 / ((4 + 1) * 200) = 7441 RPM

A measured speed value of 1 correspond to the following measurable min. actual RPM val-

ues

RPM at Min. Measurable Speed Value = 1 * 58593.75 / ((4 + 1) * 200) = 58.6 RPM

The Roborun Utility automatically makes the above calculations when setting up the

encoder.

Contents

Main Revision History Page Page SECTION 1 SECTION 2 SECTION 3 SECTION 4 SECTION 5 SECTION 6 SECTION 7 SECTION 8 SECTION 9 SECTION 10 SECTION 11 SECTION 12 SECTION 13 SECTION 14 SECTION 15 Quick Start Important Safety Warnings This product is intended for use with recharge able ba tteries What you will need Locating Switches, Wires and Connectors Connecting to the Batteries and Motors Using the Power Control Wire Connecting the R/C Radio Powering On the Controller Button Operation Default Controller Configuration Checking and Changing Configuration s Connecting the controller to your PC using Roborun Obtaining the Controllers Software Revision Number Exploring further = Software version 1.7 SECTION 2 AX2500/2850 Motor Controller Overview Product Description Technical features Page Page Page Controller Power Page Powering the Controller using the Motor Batteries Using a Backup Battery Power Fu ses Wire Length Limits Electrical Noise Reduction Techniques Power Regeneration Considerations Overvoltage Protection Undervoltage Protection Using the Controller with a Power Supply Page Page Operation Basic Operation Input Command Modes Selecting the Motor Control Modes Open Loop, Separate Speed Control Open Loop, Mixed Speed Control Closed Loop Speed Control Close Loop Position Control Tachometer or Optical Encoder (AX2850 & AX3500 only) Speed Feedback Current Limit Settings Continuous and Extended Current Lim itation Position Sensor Gear box Position Feedback Temperature-Based Current Limitation Surge Current Protection Regeneration Current Limiting Programmable Acceleration Page Command Control Curves Left / Right Tuning Adjustment Emergency Shut Down Using Controller Switches Emergency Stop using External Switch Inverted Operation Special Use of Accessory Digital Inputs Using the Inputs to Activate the Buffered Output Using the Inputs to turn Off/On the Power MOSFET transistors Self-Test Mode = Software version 1.7 Page Page Page AX2500/2850s Inputs and Outputs I/O List and Pin Assignment Connecting devices to Output C Connecting devices to Output D Connecting Switches or Devices to Input E Connecting Switches or Devices to Input F Connecting Switches or Devices to EStop/Invert Input Connecting Position Potentiometers to Analog Inputs Connecting Tachometer to Analog Inputs Connecting External Thermistor to Analog Inputs Using the Analog Inputs to Monitor External Voltages Connecting User Devices to Analog Inputs Internal Voltage Monitoring Sensors Internal Heatsink Temperature Sensors AX2500/2850 Motor Controller Users Manual 63 Temperature Conversion C Source Code FIGURE 35. Analog reading by controller vs. internal heat sink temperature Temperature Conversion C Source Code Reported Analog Value Page Fault Condition LED Messages Use of the LED Display Motor Direction Status Fault Messages No Control MOSFET Transistors are OFF Emergency Stop Self-Test Display = Software version 1.7 = Software version 2.0.c SECTION 7 R/C Operation Selecting the R/C Input Mode Typical Wiring Connector I/O Pin Assignment (R/C Mode) Pin1 8 15 9 R/C Input Circuit Description Supplied Cable Description Cabling to R/C Receiver using Full Opto-Isolation Cabling to R/C Receiver with Partial Opto-Isolation Powering the Radio from the controller Page Operating the Controller in R/C mode Reception Watchdog Important Notice about PCM Radios R/C Transmitter/Receiver Quality Considerations Joystick Deadband Programming Command Control Curves Left/Right Tuning Adjustment Joystick Calibration Automatic Joystick Calibration Activating the Accessory Outputs Data Logging in R/C Mode AX2500/2850 Motor Controller Users Manual 85 Data Logging in R/C Mode FIGURE 56. Modified R/C cable with RS232 output for data logging to a PDA GND GND Page Controls and Operation Use and benefits of RS232 Connector I/O Pin Assignment (RS232 Mode) Cable configuration TX Data Extending the RS232 Cable RX Data Data Out Data In GNDGND DB9 Female To PC Communication Settings TX Data 9600 bits/s, 7-bit data, 1 Start bit, 1 Stop bit, Even Parity Establishing Manual Communication with a PC RX Data Data Out Data In GNDGND Entering RS232 from R/C or Analog mode Data Logging String in R/C or Analog mode RS232 Mode if default RS232 Commands Set Set Motor Command Value Set Accessory Outputs Query Power Applied to Motors Query Amps Consumed by Motors Query Analog Inputs Query Heatsink Temperatures Query Battery Voltages Query Digital Inputs Read and Modify Controller Settings Apply Parameter Changes Reset Controller Optical Encoder Commands Commands Acknowledge and Error Messages Character Echo Command Acknowledgement RS-232 Watchdog RS232 Accessible Parameter Table Page Automatic Switching from RS232 to RC Mode Analog and R/C Modes Data Logging String Format : 00 11 22 33 44 55 66 77 88 99 AA BB CC Data Logging Cables Decimal to Hexadecimal Conversion Table Page Page SECTION 9 Analog Control and Operation Connector I/O Pin Assignment (Analog Mode) Connecting to a Voltage Source Connecting a Potentiometer Selecting the Potentiometer Value Analog Deadband Adjustment Power-On Safety Under Voltage Safety Data Logging in Analog Mode Page SECTION 10 Closed Loop Position Mode Selecting the Position Mode Position Sensor Selection Sensor Mounting Position Sensor Gear box Position Feedback Important Notice: Potentiometer wiring Using Optical Encoders in Position Mode Sensor and Motor Polarity Important Safety Warning Adding Safety Limit Switches Using Current Limiting as Protection Control Loop Description - PID tuning in Position Mode SECTION 11 Closed Loop Speed Mode Selecting the Speed Mode Using Optical Encoder for Speed Feedback (AX2850 only) Tachometer or Encoder Mounting Tachometer wiring Tachometer or Optical Encoder (AX2850 & AX3500 only) Speed Feedback Speed Sensor and Motor Polarity Adjust Offset and Max Speed Control Loop Description - PID tuning in Speed Mode Page Page SECTION 12 Installing, Connecting and Using the Encoder Module Optical Incremental Encoders Overview Recommended Encoder Types Installing the Encoder Module Page Connecting the Encoder Motor - Encoder Polarity Matching Voltage Levels, Thresholds and Limit Switches Wiring Optional Limit Switches Using the Encoder Module to Measure Distance Using the Encoder to Measure Speed Using the Encoder to Track Position RS232 Communication with the Encoder Module RS232 Encoder Command Set Read Encoder Counter Set/Reset Encoder Counters and Destination Registers Read Speed Read Distance Read Speed/Distance Read Encoder Limit Switch Status Read / Modify Encoder Module Registers and Parameters Important Note Page Register Description Encoder Hardware ID code Switch Status Speed or Distance 1 or 2 Counter Read/Write Mailbox Counter 1 and 2 Destination Register 1 and 2 Counter Read Data Format Encoder Testing and Setting Using the PC Utility Encoder Module Parameters Setting Exercising the Motors Viewing Encoder Data Updating the Encoder Software SECTION 13 Configuring the Controller using the Switches Programming Methods Programming using built-in Switches and Display Entering Programming Mode Changing parameters The Special Case of Joystick Calibration Restoring factory defaults Exiting the Parameter Setting Mode Programmable Parameters List Page Page Configuration Utility System Requirements Downloading and Installing the Utility Connecting the Controller to the PC Roborun Frame, Tab and Menu Descriptions Getting On-Screen Help Loading, Changing Controller Parameters Controls Settings Power Settings Analog or R/C Specific Settings Closed Loop Parameters Viewing the Parameters Summary Important Notes: Page Page Page Logging Data to Disk Connecting a Joystick Viewing and Logging Data in Analog and R/C Modes Loading and Saving Profiles to Disk Operating the AX2500/2850 over a Wired or Wireless LAN Page Updating the Controllers Software Creating Customized Object Files Page Page SECTION 15 Mechanical Specifications Mechanical Dimensions Mounting Considerations Thermal Considerations Wire Dimensions Weight